1. Field of the Invention
The present invention relates to solar collectors, e.g. solar panels and, more particularly, relates to improvements in the solar collectors.
2. Description of the Prior Art
The use of solar collectors has gained acceptance in the industry as a means of gaining "free" energy for residential and industrial applications. In a residential application, the solar panels are frequently used to provide heat for hot water to be used in the residence and also for the purpose of heating swimming pools. Other uses have also been proposed.
In industrial applications, the solar panels are frequently used to provide heat input to water used in certain processes. In some instances, the heat input may be all that is required while in other situations additional heat would be provided by a second source.
A common type of collector for solar and other radiation, used for heating water comprises an absorber plate which absorbs the radiation and transfers the resulting heat to the water. The plate or plates are usually mounted in a unit which has insulation at the back of the plate and a glass cover to prevent loss of heat such as by winds and the like.
The absorber plate will normally have one or more conduits running therethrough and through which water or an other fluid is passed. It is a well known practice to use a surface coating on the plate to enhance the absorption of the radiation and to reduce thermal radiation which all heated bodies emit (This radiation being a function of a property of the surface called emissivity). In this respect, the coating of the surface of the absorber plate is a known art and these coatings are known as selective coatings that have the property of absorbing electromagnetic radiation in a certain wave length and have a low thermal emissivity.
Various materials and processes have been proposed for the manufacture of solar panels. As aforementioned, these panels require conduits extending therethrough and to this end various proposals have been advanced in the art.
When solar panels initially started to become popular, different combinations of materials were utilized. Copper was a material of choice in view of its conductivity and its well known capability to carry domestic water without releasing toxic substances in the water flowing therethrough and to carry glycol without being attacked thereby. Copper being expensive, aluminum, a relatively good and cheaper conductor, was considered as an alternative to copper, for instance. One popular structure used a copper conduit for carrying fluid which was embedded in a plate of aluminum. However, a number of problems arose including the problem of galvanic corrosion.
To overcome these problems, many proposals have been advanced including the use of roll bonding to ensure that there was no space between the aluminum and copper with a view to eliminating the galvanic corrosion. However, this created problems of its own in that one can only use a limited size of conduit and aluminum plating. As a result, when certain fluids such glycol (required in cold locations) were used, problems would occur as the glycol would tend to break down after a few years and clog the relatively small diameter conduits. Also, the limited thickness of the aluminum plate meant that the design of the solar collector could not be optimized for maximum heat retention and transfer.
U.S. Pat. No. 4,217,886 issued to Mclaughlin on Aug. 9, 1980 discloses a radiant energy collecting element where a tool inserted through a tube extending through a helically grooved cylindrical bore of an absorber plate causes the tube to be radially expanded such that the tube cold flows into the grooves defined in the bore of the absorber plate thereby locking the tube against displacement relative to the absorber plate.